This work is designed to provide information on the mechanism of action of nerve growth factor. Nerve growth factor is a polypeptide required for the development and maintenance of the sympathetic and sensory nervous systems. Nerve growth factor controls gene expression in the neurons on which it acts. Gene expression in neuorns, and in other cells, determines the course of cellular development. A characterization of the gentic program in these cells may reveal how nerve growth factor induces the synthesis of specific enzymes and the morphological changes necessary for synapse formation. Such information would expand our knowledge of the development of the nervous system, of the tumors which arise from it, of the control of gene expression, and of the role of the growth factors. Our current studies are focused on the intracellular events which follow the binding of nerve growth factor to its membrane receptor and lead to its effect on nuclear events. We have used PC12 cells which differentiate in culture in response to nerve growth factor. Two specific phosphorylations in these cells, one cytoplasmic, the other nuclear, are altered by treatment of the cells with nerve growth factor. Both have now been observed in cell-free preparations making them both amenable to biochemical study. The cytoplasmic system has been resolved into kinase and substrate. It has been determined that the kinase is the component altered by treatment of the cells with nerve growth factor and a complete purification of the kinase is underway in order to define the molecular change responsible for the decreased activity. The phosphorylative changes in the cell are followed by changes in the structure of the DNA which may underlie changes in the transcription of specific genes. The alterations in DNA structure are being probed with specific lytic enzymes in order to correlate them temporally with changes in the expression of specific neuronal properties. The ultimate aim of our studies is to describe the actions of nerve growth factor at the molecular level, and to explore their generality in terms of other growth factors and of the developmental program of other cell types.